This header file disappeared after a pkg upgrade of libX11. Checking freshports, I see this note:
Xutil.h and extensions/XKBFile.h still use these 'XK_' prefixed symbols. So, where'd they go?
Update x11/xorgproto to 2019.2 [0]
Disable all legacy headers, they are no longer needed, since they only
detail deprecated protocol features.
Xutil.h and extensions/XKBFile.h still use these 'XK_' prefixed symbols. So, where'd they go?